Apparatus for inspecting the quality of nuclear fuel rod ends

ABSTRACT

An apparatus for inspecting the quality of both ends of nuclear fuel rods includes a housing with longitudinally separated slots for receiving X-rays downwardly therethrough to define first and second operating positions so that the forward ends of nuclear fuel rods can be aligned below the first operating position and the rear ends of nuclear fuel rods can be aligned below the second operating position. An endless conveyor belt system, having at least three longitudinally spaced apart cleats mounted thereon to define first and second film cartridge receptacles, is adapted to advance X-ray film cartridges longitudinally through the housing. A table is included for selectively lifting the film cartridges from the belt system to maintain the film cartridges stationary while the conveyor belt system is advanced. As film cartridges are advanced through the housing, they are exposed to X-rays at the first and second operating positions to image each end of a given fuel rod by initially positioning each film cartridge in the first receptacle and moving the conveyor belt to align the first receptacle with the first operating position and then transferring the film cartridge to the second receptacle by lifting the cartridge from the belt by the table and advancing the conveyor belt rearwardly to align the second receptacle and cartridge into alignment with the second operating position.

This invention relates to an apparatus and method for inspecting thequality of both ends of nuclear fuel rods and more particularly to amethod and apparatus for inspecting the quality of both ends of nuclearfuel rods by exposing the rod ends to X-rays and imaging the rod endsonto film cartridges aligned underneath the rod ends.

BACKGROUND OF THE INVENTION

The core in a nuclear reactor uses a large number of precisionmanufactured nuclear fuel rods containing fissionable pellets therein.The fuel rods typically are manufactured from open-ended tubular rodsmade from a zirconium alloy. One end of the rod is plugged with azirconium alloy end plug and girth welded by conventional tungsten inertgas methods. The fissionable pellets are inserted into the rod throughits open end which then is plugged and girth welded. Afterward, the rodis pressurized and seal welded.

Weld quality is a paramount concern in the manufacture of these rods.During fission, gas pressure builds in a fuel rod. A poor weld couldcreate a gas leak at the weld seam resulting in rod depressurization andincreased coolant radioactivity. If the rod depressurizes, the highpressure attendant the reactor core could collapse the rod creatingreactor operational problems. Thus, before the rods are inserted into areactor core, their welded ends are inspected to assure a strong weldhas been obtained.

Most nuclear fuel rods are inspected in apparatus using X-ray analysis.Typically, nuclear fuel rods are serially guided through a housinghaving a pair of longitudinally separated slots for receiving X-raysdownwardly from an external source so as to define first and secondlongitudinally spaced apart operating positions. The rods are guidedthrough the housing to a first rod position where the forward ends ofthe rods are aligned below the first operating position and to a secondrod position where the rear ends of the rods are aligned below thesecond operating position. X-ray film cartridges are serially advancedthrough the housing below the rods on an endless conveyor belt andexposed to X-rays to image each end of the fuel rod. In prior artsystems, the conveyor is operated unidirectionally and includesspaced-apart cleats for defining receptacles to hold the film cartridgestherein.

Usually, the conveyor is advanced incrementally so that multipleexposures of each rod end are taken on one film cartridge. The rods arerotated a fixed angular amount before each exposure to obtain an imageof the fuel rod end in a different orientation. Additionally, each filmcartridge is exposed to image both front and rear ends of a rod byguiding a rod from the first operating position to the second operatingposition and advancing the conveyor to move a film cartridge from thefirst to the second operating position. Multiple exposures are takenagain.

As the conveyor is advanced, one completed film cartridge is removed anda new cartridge placed onto the conveyor. The new film cartridge ispositioned on the conveyor and aligned below the first operatingposition so that simultaneous with the multiple exposure of the rear endof a first rod which has been advanced to the second operating position,the front end of a new rod which has been guided into the housing isexposed at the first operating position. The cycle continues as rods areguided through the housing and the conveyor is advanced so that exposedfilm cartridges are removed from one end of the conveyor near the secondoperating position and new film cartridges are positioned on theconveyor near the first operating position.

One drawback of the prior art practice is the error accumulationattendant any mechanical conveyor system. Each multiple exposure of arod end requires a predetermined incremental advancing of the filmcartridge below the rod end a distance at least as great as the width ofthe slot through which X-rays pass to prevent overlap of successiveexposures on the film cartridge. However, because the conveyor isunidirectional, any mechanical error is amplified. This accumulatederror makes accurate incremental positioning of a film cartridgedifficult causing overlap between exposures resulting in poor qualityX-ray images.

It is therefore an object of the present invention to provide anapparatus and method for inspecting the quality of both ends of nuclearfuel rods which overcomes the above-noted deficiencies of the prior artpractices.

It is a more particular object of the present invention to provide anapparatus and method for inspecting the quality of both ends of nuclearfuel rods wherein the mechanical error normally associated with aconveyor system used in advancing film cartridges serially through anX-ray housing of the above-noted prior art practice is minimized.

It is still another object of the present invention to provide anapparatus and method for inspecting the quality of both ends of nuclearfuel rods wherein a film cartridge positioned at a first receptacle canbe transferred to a second receptacle to eliminate the use of aunilateral conveyor system so as to minimize mechanical error.

SUMMARY OF THE INVENTION

These and other objects and advantages of the present invention areaccomplished by an apparatus and method for inspecting the quality ofboth ends of nuclear fuel rods. The apparatus includes a housing havinga pair of longitudinally separated slots for receiving X-rays downwardlytherethrough from an external source so as to define first and secondlongitudinally spaced apart operating positions. Means are included forserially guiding nuclear fuel rods longitudinally through the housing toa first rod position wherein the forward ends of the rods are alignedbelow the first operating position and to a second rod position whereinthe rear ends of the rods are aligned below the second operatingposition.

A belt conveyor assembly serially advances X-ray film cartridgeslongitudinally through the housing and below the rods so that acartridge may be selectively aligned below the first and secondoperating positions. The belt conveyor assembly comprises at least oneendless conveyor belt and at least three longitudinally spaced apartcleats mounted on the conveyor belt so as to define first and secondfilm cartridge receptacles between respective pairs of cleats. A drivemeans selectively advances the conveyor belt in opposite directions. Atable selectively lifts the film cartridges from the conveyor belt sothat the conveyor belt may be advanced while the film cartridges areheld stationary.

In operation, film cartridges are serially advanced through the housingand exposed to X-rays at each of the first and second operatingpositions. Each film cartridge is adapted to image each end of a givenfuel rod by initially positioning each cartridge in the firstreceptacle, moving the conveyor belt so that the first receptacle andcartridge are positioned in alignment with the first operating position,and then moving the film cartridge to the second receptacle by liftingthe same from the conveyor belt while advancing the conveyor beltrearwardly. The second receptacle and cartridge are then moved intoalignment with the second operating position. The table is lowered toposition the cartridge in the second receptacle.

In the preferred embodiment, the drive means is an electrical steppingmotor. Also, the belt conveyor assembly is mounted for vertical movementwith respect to the housing so as to permit the belt conveyor assemblyto be lowered to facilitate the loading and unloading of the filmcartridges. The belt conveyor assembly also includes a conveyor framehaving a top wall surface wherein the film cartridges are maintained infixed position against the conveyor housing top wall surface when thetable selectively lifts the film cartridges from the conveyor belt.

BRIEF DESCRIPTION OF THE DRAWINGS

Some of the objects and advantages of the present invention having beenstated, others will be more fully understood from the detaileddescription which follows and by reference to the accompanying drawingsin which

FIG. 1 is an end sectional view of the housing in accordance with thepresent invention showing the position of the belt conveyor assembly inthe housing.

FIG. 2 is a top plan view taken along line 2--2 of FIG. 1 and showingthe right angle drive gear motor mounting the belt conveyor assembly forvertical movement.

FIG. 3 is an enlarged sectional view of the belt conveyor assemblyshowing in detail the functional components of the assembly with thetable in its raised position.

FIG. 4 is a side sectional view of the belt conveyor assembly takenalong line 4--4 of FIG. 3.

FIG. 5 is a somewhat schematic partial cut-a-way isometric view of thebelt conveyor assembly showing in detail the relationship between thetable and the belts.

FIG. 6 is a side view of the belts showing the cleat positions forexposures 1 and 4.

FIG. 7 is a side view of the belts showing the cleat positions forexposures 2 and 5.

FIG. 8 is a side view of the belts showing the cleat positions forexposures 3 and 6.

FIG. 9 is a side view of the belts showing the cleat positions duringfilm cartridge unloading.

FIG. 10 is a side view of the belts showing the cleat positions duringfilm cartridge loading.

FIG. 11 is a side view of the belts showing the cleat positions at theinitial repeat of the exposure process for exposures 1 and 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, and more particularly to FIG. 1, theapparatus for inspecting the quality of both ends of nuclear fuel rodsin accordance with the present invention is indicated by referencenumeral 10. As will be explained in detail later, the apparatus 10includes a housing 20 having a pair of longitudinally separated slots25, 26 inside the housing for receiving X-rays downwardly therethroughfrom an X-ray generator 28 conventional to the art. The X-ray generator28 is secured to the top surface of the housing 20. Generated X-rayspass through the slots 25, 26 to define first and second longitudinallyspaced apart operating positions 30, 31.

A walking beam and roller guide assembly conventional to the art andshown schematically at 21, serially guides first and second sets ofnuclear fuel rods 35, 36 longitudinally through the housing to a firstrod position 40 where the forward ends of the rods are aligned below thefirst operating position 30 and to a second rod position 41 where therear ends of the rods are aligned below the second operating position31.

A belt conveyor assembly 50 is supported within the housing 20. Theassembly 50 serially advances first and second X-ray film cartridges 70,71 (FIG. 5) longitudinally through the housing 20 and below the rods 35,36 so that each cartridge may be selectively aligned below the first andsecond

operating positions 30, 31. As shown in FIGS. 3-5, the belt conveyorassembly 50 is formed from two parallel endless conveyor belts 51, 52entrained about two laterally directed support rods 54, 55 supported bya belt conveyor assembly frame 56. Each conveyor belt 51, 52 has threelongitudinally spaced apart cleats 57, 58, 59 mounted on the belt so asto define first and second cartridge receptacles 60, 61 betweenrespective pairs of cleats (FIG. 3). A drive motor 62 interconnects oneof the support rods 55 for selectively advancing the conveyor belts 51,52 together in either direction. A table 64 extends the length of thebelts and is adapted to selectively lift any film cartridges 70, 71 fromthe conveyor belts 51, 52 so that the conveyor belts can be advancedwhile the film cartridges are held stationary (FIG. 5).

As will be explained in more detail hereafter, film cartridges 70, 71are serially advanced through the housing 20 and exposed to X-rays ateach of the first and second operating positions 30, 31. Each filmcartridge 70, 71 is adapted to image each end of a fuel rod by initiallypositioning a first cartridge 70 in the first receptacle 60 and movingthe conveyor belts 51, 52 so that the first film cartridge 70 ispositioned in alignment with the first operating position 30. Threeexposures are taken of each rod end. After each individual exposure, theconveyor belts 51, 52 are incrementally advanced a predetermineddistance to move the film cartridge 70 so that a new unexposed portionof the cartridge underlies the rod ends. The rods are rotated 60° and anexposure is made of the rod end in a different orientation. The firstfilm cartridge 70 then is moved to the second receptacle 61 by raisingthe table 64 and lifting the film cartridge 70 from the conveyor belts51, 52 while advancing the conveyor belts 51, 52 rearwardly to align thesecond receptacle 61 with the stationary first film cartridge 70. Thetable 64 is then lowered to drop the first film cartridge 70 into thesecond receptacle 61.

A new film cartridge is placed into the now empty first film cartridgereceptacle 60. The first set of rods 35 is advanced through the housingso that the rear ends of those rods are aligned below the secondoperating position 31. A new second set of rods is advanced into thehousing so that the front ends are aligned under the first operatingposition 30. The sequence then starts again and is repeated.

Referring again to the details shown in FIG. 1, the housing 20 isrectangularly configured and fabricated from lead plates. Lead isdesirable because it absorbs X-rays and acts as a shield preventingharmful X-rays from passing through the housing to personnel positionedin close proximity thereto. The X-ray generator 28 is conventional tothe art and positioned at the top of the housing 20 where the leadshielding is minimized to allow passage of generated X-rays into thehousing. Although not illustrated in detail, the X-ray generator 28 issupported by the housing 20 and other means external to the housing. TheX-ray generator 28 is supported so that the X-ray focal plane issubstantially parallel to the conveyor belt assembly 50. The focal planecan be adjusted so that the plane of the X-ray generator is parallelwith the plane of any film cartridges by rotating conventional screwthread level adjustments 71 positioned at each lower corner between thehousing 20 and a heavy support plate 72.

Heavy roller wheels 73 are positioned at the bottom of the support plate22 to facilitate movement of the housing 20. In actual operation, thehousing 20 is positioned in a much larger frame assembly (not shown)which includes the conventional walking beam and roller assembly 21 totransport and guide fuel rods into the housing. Maintenance and repairof the apparatus 10 is facilitated because the housing 20 can be rolledfrom the frame assembly for ready accessibility thereto.

As shown schematically in FIG. 1, two opposing side walls 24 of thehousing each have an opening (not shown in detail) to facilitate guidingof a set of twenty-five fuel rods from the conventional walking beam androller assembly 21 into the housing 20. Two zirconium blocks, hereafterreferred to as a guide correction block 80, are rigidly fixed to the topof assembly 50 and positioned underlying the X-ray generator 28. Thezirconium guide correction block 80 includes apertures 81 therethroughin coaxial alignment with the openings in side walls 24 so that fuelrods may be advanced into the guide correction block 80 so as toposition the ends of fuel rods in either first or second rod positions40, 41. The guide correction block 80 is masked with lead except at twospaced-apart locations to allow generated X-rays to pass downwardlytherethrough. These two unmasked positions form the slots 25, 26 throughwhich X-rays pass. The slots 25, 26 are typically about 0.75 inches (1.9centimeters) wide and define the respective first and second spacedapart operating positions 30, 31 or "windows" through which X-rays pass.These two operating positions 30, 31 correspond to the area in the guidecorrection block 80 at which the ends of the fuel rods will bepositioned during exposure of film cartridges 70, 71 positionedthereunder.

As illustrated in FIG. 1, the belt conveyor assembly 50 is supportedwithin the housing 20 by a conventional high precision lifting mechanism90. The lifting mechanism 90 interconnects the belt conveyor assembly 50and lowers the assembly when rods are advanced through the housing orfilm cartridges are inserted or replaced. Because the film cartridgesare positioned a predetermined distance from the x-ray generator duringexposure to maintain a quality focus to image the rod ends, the liftingmechanism is precise. In the preferred embodiment, the lifting mechanismis a precision stepping gear motor 91 connecting a right angle drivesystem 92 interconnecting two precision lead screws 93 (FIGS. 1 and 2).The lead screws 93 interconnect bearing collets 94 positioned at twoopposing lower corners of the belt conveyor assembly frame 56. Tomaintain stability of the conveyor belt assembly 50, the other twoopposing corners are supported on shaft and bearing assemblies 95.

Referring now more particularly to FIGS. 3-5, there is illustrated indetail the belt conveyor assembly 50 in accordance with the presentinvention. As illustrated, the belt conveyor assembly includes aconveyor frame 56 having respective bottom and side walls surfaces 56aand 56b forming a substantially rectangular configuration thereat. Thetwo laterally directed support rods 54, 55 are rotatably mounted on twoopposing frame side walls 56b. Two endless conveyor belts 51, 52 areentrained about the support rods 54, 55 and supported thereon byconventional shaft pulleys 68. Each endless conveyor belt 51, 52 isapproximately 2.5 centimeters wide and formed from a material havingsufficient resiliency and strength such as rubber. As illustrated inFIG. 5, at least three cleats 57, 58, 59 are positioned on each beltwith the cleats on one belt positioned in corresponding relation withcleats of the other belt so as to define the first and second filmcartridge receptacles 60, 61 extending transverse to the belts andbetween respective pairs of cleats. The cleats 57, 58, 59 can beattached to the belts 51, 52 by means conventional to the art such asmechanical fasteners or adhesives. As illustrated, first and second filmcartridges 70, 71 rest on the belts 51, 52 between the cleats. A filmcartridge typically is 5 inches (13 centimeters wide), 17 inches (43centimeters long), and 0.19 inches (0.5 centimeters) thick and formedfrom a two ply paperboard having an X-ray sensitive film insertedtherebetween. The film cartridges are placed manually into the filmreceptacles when the belt conveyor assembly 50 is in its loweredposition. A lead door (not shown) on the housing 20 provides access toan opening (not shown) fabricated in the belt conveyor assembly frame 56to permit placement of film cartridges in the receptacles 60, 61.

In the preferred embodiment the drive motor 62 is a stepping motor andinterconnects the second support rod 55 via a belt transmission 63 toprovide accurate and incremental advancing of the conveyor belts 51, 52in either a forward or reverse direction. As will be explained in detailhereafter, the stepping motor provides accurate advancement of the filmcartridges 70, 71 positioned under the respective first or secondoperating positions 30, 31 to allow multiple exposures. The steppingmotor 62 is operated by a controlled numologic. Each revolution of themotor shaft corresponds to 12,800 incremental steps, thus maintaininghigh accuracy in belt positioning. After each exposure, the conveyorbelts 51, 52 are advanced approximately 0.75 inches (1.9 centimeters) toposition a clear, unexposed portion of a film cartridge in the 0.75inches (1.9 centimeter) wide operating position or "window" formed bythe slots 25, 26. When a film cartridge has been exposed, six parallelrows of images are produced thereon corresponding to three exposureseach of front and rear ends of a fuel rod.

As best illustrated in FIG. 5, a table 64 extends longitudinally in thebelt conveyor assembly 50 and is supported by the belt conveyor assemblyframe 56. The table 64 can be raised or lowered by pistons 66interconnecting the frame 65 with the belt conveyor assembly framebottom surface 56a. The table 64 includes three plates 64a secured tothe table frame 65. The plates 64a are positioned to form at least twochannels 67 having the conveyor belts 51, 52 in association therewith.Thus, the table 64 can be lowered or raised so that the top portions ofthe conveyor belts 51, 52 extend above or below the plates 64a. Asillustrated in FIG. 5, the table is in a lowered position with the topportion of the belts extending above the plates 64a. The film cartridges70, 71 rest on the conveyor belts 51, 52 allowing incremental advancingof the belts and cartridges.

The table 64 serves a dual function. First, during exposure, it isnecessary to place the film cartridges in a fixed position relative tothe fuel rod ends to maintain adequate focusing during exposure. Becausethe conveyor belts 51, 52 have a certain resiliency to them, thedistance between the film cartridges 70, 71 resting on the belts and thefuel rod ends will vary. This problem is solved by the function of thetable 64. At each exposure, the table 64 is raised to lift the filmcartridges 70, 71 off the belts 51, 52 and press the film cartridgesagainst the lower surface of the guide correction block 80 positioned ontop of the belt conveyor assembly 50. Because each film cartridge iscompressed against a rigid surface, the film cartridges 70, 71 arepositioned a predetermined distance from the fuel rod ends positioned atfirst and second operating portions 30, 31.

Second, the table 64 is used in the shuttling sequence where a filmcartridge is transferred from the first film cartridge receptacle 60 tothe second film cartridge receptacle 61. A cartridge positioned in thefirst film cartridge receptacle 60 is lifted from the conveyor belts 51,52 so that the belts can be reversed to position the second filmcartridge receptacle 61 in alignment with the film cartridge resting onthe table. When the table 64 is lowered, the film cartridge also islowered into the second film cartridge receptacle 61. A new filmcartridge is placed into the now empty first film cartridge receptacle60. Thus, movement of the conveyor belts 51, 52 is not completelyunilateral and the accumulated mechanical error often present with priorart practices is avoided.

Referring now to FIGS. 6-11, the relative positions of the cleats 57,58, 59 during loading, unloading and imaging rod ends in accordance withthe present invention are shown. For purposes of illustration only, onlyone rod instead of a full set of twenty-five rods will be referred tohereafter. Six exposures are made of a fuel rod--three exposures of thefront end of the rod and three exposures of the rear end of the rod.After each exposure, the rod is rotated 60° so that an exposure of eachrod end in a different orientation is made. Although more exposures ofeach rod end could be produced if a larger film cartridge was used,three exposures of each end have been found sufficient to give adequateimaging of a fuel rod end and determine defects therein.

FIG. 6 illustrates the cleat positions for Exposure Numbers 1 and 4.Exposure 1 corresponds to the first exposure of a first film cartridgepositioned in the first film cartridge receptacle 60 to image the frontend of a first fuel rod 35. Exposure 4 corresponds to the fourthexposure of a second film cartridge positioned in the second filmcartridge receptacle 61 to image the rear end of a second fuel rod 36.The film cartridge positioned in the second receptacle 61 already hasbeen exposed three times to image the front end of that second rod 36when it previously had been positioned in the first rod position 40.

At this time, the table 64 is extended to press the film cartridgesagainst the guide correction block 80. The X-ray generator 28 isactivated and X-rays pass through the slots 25, 26 to image on the firstfilm cartridge 70 the front end of the first fuel rod 35, andconcurrently image on the second film cartridge the rear end of thesecond fuel rod 36. To prevent overlap on the second film cartridgebetween the fourth exposure and the first, second or third exposures,the second slot 26 is machined in the guide correcting block 80 toposition the slot 26 so that the X-rays passing therethrough aredelivered on the second film cartridge rearwardly of parallel exposures1, 2 and 3.

After the first and fourth exposures, the table 64 is lowered so thatthe film cartridges are resting on the belts between respective pairs ofcleats 57, 58, 59. The conveyor belts 51, 52 are advanced forwardapproximately 0.75 inches (1.9 centimeters) (FIG. 7) and the rodsrotated 60°. The table 64 is raised again to press the film cartridgesagainst the guide correction block 80. The second and fifth exposuresare taken. Because the actual slots 25, 26 or "windows" through whichthe X-rays pass are 0.75 inches (1.9 centimeters) wide, and the conveyorbelts 51, 52 have advanced approximately 0.75 inches (1.9 centimeters),the first and second, and fourth and fifth images do not overlap. Thetable 64 is lowered again to rest the film cartridges on the conveyorbelts. The belts are advanced another 0.75 inches (1.9 centimeters) andthe rods 35, 36 rotated another 60°. The table 64 is raised again andthe third and sixth exposures made (FIG. 8).

After the sixth exposure, the film cartridge positioned in the secondfilm cartridge receptacle 61 is now complete having six parallelexposures corresponding to three exposures each of respective front andrear ends. This cartridge is removed from the housing 20. The first filmcartridge having only three exposures of the front end of a rod istransferred to the second film cartridge receptacle 61.

To transfer and remove respective first and second film cartridges asdescribed above, the conveyor belt assembly 50 is lowered and the secondrod 36 advanced from the housing 20 and conveyed by the walking beam androller guide assembly 21 to another area for future processing. Thefirst rod 35 is advanced through the housing 20 and positioned outsidethe housing adjacent the second operating position 31. The conveyorbelts are forwardly advanced approximately 3 inches (7.5 centimeters)and the film cartridge positioned in the second film cartridgereceptacle removed (FIG. 9). The table 64 is extended to raise the filmcartridge positioned in the first receptacle 60 from the conveyor belts51, 52. The conveyor belts 51, 52 are reversed approximately 5.5 inches(14 centimeters) so that the second film cartridge receptacle 61 isaligned with the film cartridge positioned on the table. This positionof alignment is indicated on FIG. 10 by cleat positions 58' and 59'

The table 64 is lowered to place the first film cartridge between cleats58, and 59, The conveyor belts 51, 52 are reversed again approximately 5centimeters and a new film cartridge positioned on the conveyor belts sothat the leading edge of the new film cartridge is set against cleat 58(FIG. 10). The first fuel rod 35 is advanced back into the housing sothat its rear end is aligned under the second operating position 31. Anew fuel rod is advanced into the housing 20 so that its front end isaligned under the first operating position 30. The belt conveyorassembly 50 is raised and the conveyor belts 51, 52 advanced to alignthe film cartridges under the respective operating positions. The cycleis then repeated.

The foregoing embodiment is to be considered illustrative, rather thanrestrictive of the invention and the modifications which come within themeaning and range of equivalents of the claims are to be includedtherein.

That which is claimed is:
 1. An apparatus for inspecting the quality ofboth ends of nuclear fuel rods and comprisinga housing including a pairof longitudinally separated slots for receiving X-rays downwardlytherethrough from an external source and so as to define first andsecond longitudinally spaced apart operating positions, means forserially guiding nuclear fuel rods longitudinally through said housingand to a first rod position wherein the forward ends of the rods arealigned below said first operating position and to a second rod positionwherein the rear ends of the rods are aligned below said secondoperating position, belt conveyor assembly means for serially advancingX-ray film cartridges longitudinally through said housing and below saidrods, and so that each cartridge may be selectively aligned below saidfirst and second operating positions, said belt conveyor assembly meanscomprising at least one endless conveyor belt, at least threelongitudinally spaced apart cleats mounted on said conveyor belt and soas to define first and second film cartridge receptacles betweenrespective pairs of cleats, drive means for selectively advancing saidconveyor belt in opposite directions, and table means for selectivelylifting the film cartridges from said conveyor belt and so that theconveyor belt may be advanced while the film cartridges are heldstationary, whereby film cartridges may be serially advanced throughsaid housing and exposed to X-rays at each of said first and secondoperating positions and so that each film cartridge is adapted to imageeach end of a given fuel rod, by initially positioning each cartridge insaid first receptacle, moving the conveyor belt so that said firstreceptacle and cartridge are positioned in alignment with said firstoperating position, moving the film cartridge to said second receptacleby lifting the same from said conveyor belt while advancing the conveyorbelt rearwardly, and then moving the second receptacle and cartridgeinto alignment with said second operating position.
 2. The apparatus asdefined in claim 1 wherein said drive means includes an electricalstepping motor.
 3. The apparatus as defined in claim 1 furthercomprising means mounting said belt conveyor assembly means for verticalmovement with respect to said housing and so as to permit said beltconveyor assembly means to be lowered to facilitate the loading andunloading of film cartridges therefrom.
 4. The apparatus as claimed inclaim 1 wherein said belt conveyor assembly means includes a top wallsurface positioned so that said film cartridges are maintained in fixedposition against said top wall surface when said table means selectivelylifts film cartridges from said conveyor belt.
 5. The apparatus asclaimed in claim 1 including means positioned along the bottom of saidhousing for facilitating movement of said housing.
 6. The apparatus asclaimed in claim 1, wherein said housing is formed of lead.
 7. Anapparatus for inspecting the quality of both ends of nuclear fuel rodsand comprisinga housing including a pair of longitudinally separatedslots for receiving X-rays downwardly therethrough from an externalsource and so as to define first and second longitudinally spaced apartoperating positions, means for serially guiding nuclear fuel rodslongitudinally through said housing and to a first rod position whereinthe forward ends of the rods are aligned below said first operatingposition and to a second rod position wherein the rear ends of the rodsare aligned below said second operating position, belt conveyor assemblymeans for serially advancing X-ray film cartridges longitudinallythrough said housing and below said rods, and so that each cartridge maybe selectively aligned below said first and second operating positions,said belt conveyor assembly means including a conveyor frame having twoopposing side wall surfaces, at least two laterally directed supportrods rotatably mounted to said opposing side wall surfaces, at least twoendless conveyor belts entrained about said support rods in spacedrelation to each other, at least three longitudinally spaced apartcleats mounted on each conveyor belt and so as to define first andsecond film cartridge receptacles extending transverse to said belts andbetween respective pairs of cleats so that said belts support a filmcartridge positioned thereon, drive means supported by said conveyorframe and operatively engaging select ones of said support rods forselectively advancing said conveyor belt in opposite directions, andtable means supported by said conveyor frame for selectively lifting thefilm cartridges supported by said belts and so that the conveyor beltsmay be advanced while the film cartridges are held stationary, wherebyfilm cartridges may be serially advanced through said housing andexposed to X-rays at each of said first and second operating positionsand so that each film cartridge is adapted to image each end of a givenfuel rod, by initially positioning each cartridge in said firstreceptacle, moving the conveyor belts so that said first receptacle andcartridge are positioned in alignment with said first operatingposition, moving the film cartridge to said second receptacle by liftingthe same from said conveyor belts while advancing the conveyor beltsrearwardly, and then moving the second receptacle and cartridge intoalignment with said second operating position.
 8. The apparatus asclaimed in claim 7 wherein said conveyor frame includes a top wallsurface positioned so that said film cartridges are maintained in fixedposition against said top wall surface when said table means selectivelylifts the film cartridges from said conveyor belts.
 9. The apparatus asclaimed in claim 7 wherein said table means includes means operativelyengaging said conveyor frame for providing lift to said table means. 10.The apparatus as claimed in claim 7 wherein said table means includes atleast two longitudinally extending channels extending the length of saidbelts, and wherein said channels are positioned so that said belts arein association with said channels so that said table means can retractbelow the top portion of said belts.